The user profile image is broken in Gmail in the notification mail for a private wiki

In a standard event displayer, below the page name/link you have a line with "edited by " followed by the user image and its name/link.

The problem is that, when the wiki is private, the image does not work.

I indicated Gmail because that's my use case, but I assume the same is true for various mail clients and especially for non browser based mail clients (but it might work on some browser based mail clients which are less inclined to sanitize the mails than Gmail).